Method for transmitting and/or receiving audio signals

ABSTRACT

A method for transmitting and/or receiving a potential aggressor audio signal includes a transmission and/or a reception of successive groups of data timed by a first clock signal within respective successive frames synchronized by a second clock signal. In the presence of a risk of interference of the potential aggressor audio signal with a different, potential victim, signal, during the transmission or reception of the potential aggressor audio signal, the frequency of the first clock signal is modified while keeping the frequency of the second clock signal unchanged.

This application claims the priority to French Application No. 1550952,filed on Feb. 6, 2015, which application is hereby incorporated hereinby reference.

TECHNICAL FIELD

Embodiments of the invention relate to the transmission of an audiosignal and, in particular embodiments, include a frequency evasionmechanism of the transmission clock.

BACKGROUND

In a cellular mobile telephone or wireless communication deviceincluding a plurality of reception/transmission circuits, the digitalinterfaces normally generate interference which adversely affects theradiofrequency transmitters and which causes a degradation in thereceived signals and therefore a degradation in the receive performance.These digital interfaces are regarded as “aggressors.”

The digital audio signal transmitters/receivers generate interference,notably due to electromagnetic leakage. FM radio receivers are verysensitive to this electromagnetic leakage because, inter alia, FM radiosoperate at quite low frequencies, notably between 65 and 108 MHz.

FM radio receivers are not the only “victims.” In fact, 2G and 3Gtransmitters and/or receivers are also potential victims, as is the GPS(Global Positioning System) network, but also phase locked loops,denoted PLL, amplifiers, analog/digital or digital/analog converters,etc.

More generally, any electronic device containing sensitive analog partsmay fall victim to interference.

The 2G or 3G bands are higher. The minimum lower limit of these bandshas a frequency of 450 MHz. Consequently, interference should not be asgreat. However, this interference may nevertheless cause seriousproblems for signal reception.

Moreover, digital audio interfaces may be considered as aggressors forsome electronic devices which are then considered as potential victims.

SUMMARY

Embodiments of the invention relate to the transmission of an audiosignal and, more particularly, the reduction in the interferencegenerated by the potential “aggressor” audio signal on other signalstransmitted or received by neighboring transmitters/receivers which areregarded as “victims.”

Different approaches exist for reducing this interference.

A first approach consists in acting directly on the routing of thetracks on the printed circuits, notably by distancing to the maximum thetracks of the potential victims in order to reduce electromagneticinteractions and capacitive coupling. The major disadvantage of thisapproach is the surface cost and the complexity brought about or addedto an already fundamentally complex task. Some printed circuits havelimited dimensions and a high number of tracks which limits thepossibilities of such an approach.

A second approach, referred to as “slew-rate control” or “slew-ratelimitation”, consists in using electronic circuitry in order to modifythe initial, segmented shape of the digital audio signal and notablyapply a slope to the rising and falling edges of the signal. Thisapproach enables the interference to be reduced, but without evereliminating it. Given the modification made to the shape of the signal,the reduction in the interference is implemented to the detriment of theintegrity of the signal or sampling speed in the case where theintegrity of the signal needs to be preserved. The “slew-ratelimitation” technique does not work well for victims sensitive to lowfrequencies.

According to one embodiment, a third approach, different from the othertwo presented approaches, enables the interference to be reduced or eveneliminated by acting directly on the frequency of an “aggressor” digitalaudio signal without affecting the perception thereof.

According to one aspect, a method for transmitting and receiving apotential aggressor audio signal is proposed, the method comprising atransmission and/or a reception of successive groups of digital audiodata timed by a first clock signal within respective successive framessynchronized by a second clock signal, typically corresponding to therhythm of the frame (“frame synchronization”).

According to one general characteristic of this aspect, in the presenceof a risk of interference of the potential aggressor audio signal with adifferent, potential victim, signal, during the transmission orreception of the potential aggressor audio signal, the frequency of thefirst clock signal is modified while keeping the frequency of the secondclock signal unchanged.

The modification (increase or decrease) of the frequency of the firstclock signal which corresponds to the data transmission frequency of theaudio signal enables the implementation of a frequency offset of theaudio signal in relation to the frequency band to which the victim issensitive and therefore the separation into two distinct frequencies ofthe elements of each signal, thus eliminating any interference.

The modification of the frequency of the first clock signal can belikened to a transmission clock frequency hopping mechanism.

The maintenance of the frequency of the second clock signalcorresponding to the reading or writing frequency of the potentialaggressor audio signal enables the avoidance of any modification of thesound heard by the user of the potential aggressor audio signal. Infact, a modification of the audio reading frequency would modify theauditory perception of the audio signal by a sound being lower or higherand therefore altered. In more extreme cases, clips or pops may beobserved, since the device transforming the electric signal into anacoustic signal will receive too many or not enough samples.

The method applies as much to a “master” audio transmitter as to a“master” audio receiver, the “master” component (transmitter orreceiver) fixing the transmission/reception frequencies of the “slave”component (receiver or transmitter.

In fact, the “master” electronic component modifies the frequency of itsfirst clock signal and the “slave” electronic component, given that itoperates with the same clocks as the “master” electronic, then operateswith the modified frequency.

Given the non-modification of the frame synchronization frequency, thismethod complies with the I²S electrical interface standard, alsoreferred to as “Integrated Interchip Sound.” The I²S standard is aserial bus electrical interface standard for connecting digital audiodevices together. More generally, this method is also well suited tomultichannel audio protocols, such as TDM (Time Division Multiplexing).

Advantageously, the method may include an evaluation of the interferencerisk of the potential aggressor audio signal with the other, potentialvictim, signal having a carrier frequency, the evaluation including acomparison of the harmonics of the frequency of the first clock with thefrequency plan to be preserved.

The evaluation allows the appearance of interference on the other,potential victim, signals to be anticipated. The evaluation is carriedout on the basis of the frequencies used by the different “victim”transmitters/receivers and on the basis of the frequencies used by thedifferent “aggressor” transmitters/receivers.

The group of data is preferably transmitted within each frame within aprocessing time window having a length less than or equal to the periodof the second clock.

The definition of a processing time window within a period of the secondclock enables the synchronization with each new frame of the audio datato be transmitted with the corresponding frame.

The time window may advantageously begin on the active edge of thesignal of the first clock preceding the active edge of the signal of thesecond clock, the data of the group of data of the audio signal beingtransmitted from the active edge of the signal of the first clocksimultaneously with the active edge of the signal of the second clock.

The starting of the time window within a period of the first clockbefore the active edge of the second clock ensures the correctsynchronization of the first and second clocks, regardless of the typeof transmitter/receiver, notably when the frequency of the first clockhas been modified between two activities of the signal of the secondclock.

The signal of the first clock and the signal of the second clock canadvantageously be constructed from the signal of the same main clock,the signal of the first clock resulting from a first division of thesignal of the main clock and the signal of the second clock resultingfrom a second division of the signal of the main clock.

This configuration allows the frequency of the signal of the first clockto be modified independently from the frequency of the signal of thesecond clock.

Alternatively, the signal of the first clock and the signal of thesecond clock can be constructed from the signal of the same main clock,the signal of the first clock resulting from a division of the signal ofthe main clock, and the signal of the second clock resulting from adivision of the signal of the first clock.

In this configuration, when the frequency of the signal of the firstclock is modified, the second divider is modified in such a way as tokeep the frequency of the signal of the second clock unchanged. Thefrequency of the signal of the first clock is therefore chosen frommultiples of the frequency of the signal of the second clock.

According to a different aspect, a system is proposed for transmittingand receiving a potential aggressor audio signal including a first clocksuitable for timing at a first frequency the transmission and/orreception of successive groups of data within respective successiveframes and a second clock suitable for timing the frames at a secondfrequency.

According to a general characteristic of this aspect, the systemincludes a controller configured in such a way that, in the presence ofa risk of interference of the potential aggressor audio signal with avictim device processing a different, potential victim, signal, theymodify the frequency of the first clock signal by keeping the frequencyof the second clock signal unchanged.

The system may advantageously include an evaluation circuit configuredto evaluate the risk of interference of the potential aggressor audiosignal with the other, potential victim, signal having a carrierfrequency, the evaluation circuit including a comparator suitable forcomparing the harmonics of the frequency of the first clock with thecarrier frequency of the other, potential victim, signal.

The system may advantageously include a main clock, a first frequencydivider connected to the output of the main clock and suitable fordelivering the signal of the first clock, and a second frequency dividerconnected to the output of the main clock and suitable for deliveringthe signal of the second clock.

Alternatively, the system may include a main clock, a frequency dividerconnected to the output of the main clock and suitable for deliveringthe signal of the first clock on a first output, and a frequency dividerconnected to a second output of the first clock and suitable fordelivering the signal of the first clock.

According to a further different aspect, a communication device, inparticular a cellular mobile telephone, is proposed, incorporating asystem as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics of the invention will becomeevident from the detailed description of an embodiment of the invention,which is in no way limiting, and the attached drawings, in which:

FIG. 1 shows a flow diagram of a transmission method according to oneembodiment of the invention;

FIG. 2 shows a graphical representation of signals transmitted with andwithout modification of the frequency of the first clock signal of themethod shown in FIG. 1; and

FIG. 3 shows schematically a system for transmitting an audio signalaccording to one embodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a flow diagram of a method for transmitting a potentialaggressor audio signal according to one embodiment of the invention, thetransmission being considered here as the “master” element.

In a first step 100 of the transmission method, a group of N audio databits is received. A group of N audio data bits is received by aprocessing unit with each new period of a signal of a synchronizationclock 4, the frequency of which corresponds to the frequency of theframe, i.e. the frequency at which the audio data are subsequently read.

Instead of receiving a single group of N bits, the method could includea reception of a plurality of groups simultaneously, the groupsincluding a variable number of bits.

The potential aggressor audio signal is transformed in order to transmitthe audio data. Each group of N bits is transformed into a succession ofN bits. In fact, the N audio data bits of a group are received inparallel and are serialized before their transmission. The N bits of agroup are serialized at a transmission frequency SCK higher than thesynchronization frequency SYNC. The transmission frequency SCK is chosenin such a way as to transmit all of the N bits of at least one groupwithin the same period, i.e. the same frame, of the synchronizationclock signal.

Before performing the serialization (serialisation), a comparison iscarried out, in a step 110, of the harmonics of the transmissionfrequency SCK provided to transmit the N bits of the frame at theworking frequencies of the transmitter/receivers likely to be victimsincluded in the electronic device in which the transmission systemcarrying out the method is installed.

If harmonics of the transmission frequency SCK correspond to the workingfrequency of one of the other transmitters/receivers of the potentialvictim device, the transmission frequency SCK of the data is modified ina step 120. The frequency is modified by changing the frequency inrelation to the minimum necessary frequency.

The minimum necessary frequency corresponds to the minimum frequencyenabling the transmission of the N audio data bits of a group in aframe, i.e., in a period, of the signal of the synchronization clock 4.

The data transmission frequency SCK is thus chosen so that none of itsharmonics, or as few harmonics as possible, correspond to one of theworking frequencies of the victim devices.

Once the transmission frequency SCK has been selected, the data of thegroup are transformed in a step 130. The N data are thus serializedinitially in parallel in such a way as to obtain a series of N bitstimed at the transmission frequency SCK thus selected.

A processing time window F is generated in a following step 140. Theprocessing time window F is generated on the active edge of the periodof the signal of the transmission clock 3 preceding the active edge ofthe signal of the synchronization clock 4.

The frequency change of the signal of the transmission clock 3 isimplemented on the active edge of the signal of the synchronizationclock 4. Also, in the case where the transmission frequency SCK ismodified between two frames of the signal of the synchronization clock4, the first period of the signal of the transmission clock 3 in thetime window F, i.e., the period of the signal of the transmission clock3 preceding the active edge of the synchronization clock 4, is differentfrom the value of the following periods.

The audio data of a group are transmitted within this time window F andwithin a frame of the signal of the synchronization clock 4.Consequently, during the first period of the signal of the transmissionclock 3 in the time window F, no datum of the group is transmitted.

This time lag in the starting of the transmission window ensures thecorrect synchronization of the transmission clock 3 with thesynchronization clock 4, regardless of the transmitter that is used.

Finally, in a step 150, the series of N audio data bits of a group istransmitted at a transmission frequency SCK within the frame of thesignal of the synchronization clock 4, and within the time window F.

As illustrated in FIG. 2, which shows a graphical representation of thesignals of the two clocks SCK and SYNC of the time window F, the timewindow is closed before the end of the frame of the signal of thesynchronization clock 4 and before the opening of a new time frame F.

Alternatively, it is possible to provide a closing of the preceding timewindow F coinciding with the opening of the following time window F.

Moreover, as can be seen, the opening of the time window F beingsynchronized with the signal SCK of the transmission clock 3, the timeof opening of the time window F varies in relation to the signal SYNC ofthe synchronization clock 4.

In a different embodiment of the invention, the method can be applied tothe reception of an audio signal, the reception being the “master”element.

In an embodiment of this type, the consequence of the modification ofthe frequency of the first clock signal by the receiver is that the“slave” transmitter will transmit the signal with the modified frequencyof the first clock signal.

FIG. 2 also includes an example of a graphical representation (timingchart at the bottom of FIG. 2) of a signal SCK of the transmission clock3 in the case where it would not be synchronized with the time window F.

FIG. 3 shows schematically a system for transmitting an audio signalaccording to one embodiment of the invention, suitable for carrying outthe method shown in FIG. 1.

A system of this type can be incorporated within a communication device,for example, a cellular mobile telephone or a router, etc.

The transmission system 1 includes a number of circuits. An acquisitioncircuit 2 acquires an audio signal that comprises a succession of groupsof audio data. A transmission clock 3 is suitable for timing at atransmission frequency SCK the transmission of successive groups of datawithin respective successive frames. A synchronization clock 4 issuitable for timing the frames at a synchronization frequency SYNC.

The signals of each clock are generated from the same signal of a mainclock 5.

The transmission clock 3 includes a first divider suitable for applyinga frequency division coefficient to the signal received at the input ofthe transmission clock 3 and originating from the main clock 5.

The synchronization clock 4 includes a second divider suitable forapplying a frequency division coefficient to the signal received at theinput of the synchronization clock 4 and originating from the main clock5.

The system 1 furthermore includes evaluation circuit 6, which isconfigured to evaluate the interference risk of the potential aggressoraudio signal with the victim device processing a different signal havinga carrier frequency. The evaluation circuit 6 includes a comparatorsuitable for comparing the harmonics of the frequency SCK of thetransmission clock 3 with the carrier frequency of the other signal.

The system 1 also includes controller 7 configured in such a way that,in the presence of a risk of interference of the audio signal with avictim device processing a different signal, the controller 7 modifiesthe frequency of the transmission clock signal 3 while keeping thefrequency of the synchronization clock 4 unchanged.

In the case where the frequency of the signal of the transmission clock3 is modified for the first time, the frequency will generally beincreased. Conversely, in the case where this frequency has already beenpreviously modified, it may be increased or reduced in order to reducethe risk of interference, provided that it is not lower than the minimumauthorized frequency below which a malfunction occurs.

As indicated above, the minimum necessary frequency corresponds to theminimum frequency enabling the transmission of the N audio data bits ofa group in a frame, i.e. in a period, of the signal of thesynchronization clock 4.

The system 1 includes transmitter 8, connected to the transmission clock3 and to the synchronization clock 4, and receiving at the input thegroups of audio data bits delivered by the acquisition circuit 2.

The transmitter 8 include a data serialization module 9 suitable fortransforming the groups of audio data in parallel and a series of databits timed at the transmission frequency SCK of the transmission clock 3in a frame of the signal of the synchronization clock 4.

The transmitter 8 furthermore include a module 10 for generating aprocessing time window F configured to generate a time window F in whichthe audio data must be transmitted.

The system and method for transmitting and/or receiving a potentialaggressor audio signal enable a reduction or even elimination of theinterference generated by electromagnetic leakage of the audio signal inan electronic device by acting directly on the transmission frequency ofthe audio signal, but without modifying the audio signal readingfrequency.

What is claimed is:
 1. A method for communicating, the methodcomprising: communicating successive groups of digital data timed at afirst frequency by a first clock signal within respective successiveframes synchronized at a second frequency by a second clock signal, thecommunicating comprising transmitting or receiving a potential aggressorsignal; and modifying the first frequency while keeping the secondfrequency unchanged while communicating the potential aggressor signal,the modifying performed in the presence of a risk of interference of thepotential aggressor signal with a potential victim signal, wherein atime window for transmitting the digital data begins on an active edgeof the first clock signal that precedes an active edge of the secondclock signal, the data of the groups of data being communicated from theactive edge of the first clock signal simultaneously with the activeedge of the second clock signal.
 2. The method according to claim 1,wherein the digital data comprises digital audio data and wherein thepotential aggressor signal comprises a potential aggressor audio signal.3. The method according to claim 1, further comprising evaluating therisk of interference of the potential aggressor signal with thepotential victim signal.
 4. The method according to claim 3, wherein theevaluating comprises comparing harmonics of the first frequency with afrequency plan of potential victim devices likely to be affected byinterference.
 5. The method according to claim 1, wherein thecommunicating comprises transmitting the potential aggressor signal. 6.The method according to claim 1, wherein the communicating comprisesreceiving the potential aggressor signal.
 7. The method according toclaim 1, wherein the groups of data are communicated within each framewithin a processing time frame that has a length less than or equal to aperiod of the second clock signal.
 8. The method according to claim 1,wherein the first clock signal and the second clock signal are bothgenerated from a main clock signal, the first clock signal resultingfrom a first division of the main clock signal and the second clocksignal resulting from a second division of the main clock signal.
 9. Themethod according to claim 1, wherein the first clock signal and thesecond clock signal are generated from a main clock signal, the firstclock signal resulting from a first division of the main clock signaland the second clock signal resulting from a division of the first clocksignal.
 10. A system for transmitting and receiving signals, the systemcomprising: a first clock generator configured to generate a first clocksignal that is suitable for timing communication of successive groups ofdata within respective successive frames at a first frequency; a secondclock generator configured generate a second clock signal to time theframes at a second frequency; and a controller configured to modify thefirst frequency while the second frequency remains unchanged in thepresence of a risk of interference with a potential victim signal duringthe communication, wherein the controller is further configured togenerate a time window for transmitting the data that begins on anactive edge of the first clock signal that precedes an active edge ofthe second clock signal, the data of the successive groups of data beingcommunicated from the active edge of the first clock signalsimultaneously with the active edge of the second clock signal.
 11. Thesystem according to claim 10, further comprising an evaluation circuitconfigured to evaluate the risk of interference with the potentialvictim signal.
 12. The system according to claim 11, wherein theevaluation circuit comprises a comparator configured to compareharmonics of the first frequency of the first clock signal with afrequency plan of devices likely to be affected by interference.
 13. Thesystem according to claim 10, further comprising a main clock circuit;wherein the first clock generator comprises a first frequency dividerwith an input coupled to an output of the main clock circuit; andwherein the second clock generator comprises a second frequency dividerwith an input coupled to the output of the main clock circuit.
 14. Thesystem according to claim 10, further comprising a main clock circuit;wherein the first clock generator comprises a first frequency dividerwith an input coupled to an output of the main clock circuit; andwherein the second clock generator comprises a second frequency dividerwith an input coupled to an output of the first frequency divider.
 15. Acellular mobile telephone comprising the system according to claim 10.16. A system comprising: a main clock circuit configured to generate amain clock signal; a transmission clock circuit configured to generate atransmission clock signal based on the main clock signal; asynchronization clock circuit configured to generate a synchronizationclock signal based on the main clock signal; a transmitter with a clockinput coupled to receive the transmission clock signal, the transmitterconfigured to transmit a potential aggressor signal; an evaluationcircuit configured to evaluate a risk of interference of the potentialaggressor signal with a potential victim signal; and a controllerconfigured to modify a frequency of the transmission clock signal in thepresence of a risk of interference with the potential victim signalduring transmission of the potential aggressor signal, wherein afrequency of the synchronization clock signal remains unchanged duringtransmission of the potential aggressor signal, and wherein thecontroller is configured to generate a time window for transmitting thepotential aggressor signal, the time window beginning on an active edgeof the transmission clock signal that precedes an active edge of thesynchronization clock signal, the potential aggressor signal beingcommunicated from the active edge of the transmission clock signalsimultaneously with the active edge of the synchronization clock signal.17. The system according to claim 16, wherein the evaluation circuitcomprises a comparator configured to compare harmonics of the frequencyof the transmission clock signal with a frequency plan of devices likelyto be affected by interference.
 18. The system according to claim 16,wherein the transmission clock circuit comprises a first frequencydivider with an input coupled to an output of the main clock circuit,and wherein the synchronization clock circuit comprises a secondfrequency divider with an input coupled to the output of the main clockcircuit.
 19. The system according to claim 16, wherein the transmissionclock circuit comprises a first frequency divider with an input coupledto an output of the main clock circuit, and wherein the synchronizationclock circuit comprises a second frequency divider with an input coupledto an output of the first frequency divider.